The composition and application of solid electrolyte electrochemical cells as oxygen sensors have been described in detail in prior art publications including reissue patent Re. 28,792 which is assigned to the assignee of the present invention and is incorporated herein by reference.
The operation of many conventional solid electrolyte oxygen sensors requires the presence of a reference oxygen source which typically is either a gas or a metal/metal oxide mixture. The necessity for an oxygen reference increases the design complexity and cost of many conventional solid electrlyte oxygen sensors.
Resistor-type oxygen sensors are also well known in the art. The resistor-type oxygen sensor typically consists of a semiconducting metal-oxide which experiences a change in the electronic structure caused by a change in the stoichiometry of the oxide. A reducing atmosphere causes oxygen deficiencies in the metal-oxide lattice of the conventional resistor-type oxygen sensor. A free oxygen containing atmosphere on the other hand can cause excess oxygen in the lattice. In other words, the oxygen concentration in the surrounding atmosphere can produce mass changes in the conventional resistor-type oxygen sensor. This results in insufficient response times and accuracy.
The application of a mixed valence oxide compound as a resistor-type solid state oxygen sensor is disclosed in detail in U.S. Pat. No. 3,558,280, entitled "Solid State Oxygen Gauge", issued Jan. 26, 1971, assigned to the assignee of the present invention and incorporated herein by reference.